Compounds for reducing ultraviolet degradation of a variety of substrates are known and have been used in many fields, including topical skin creams, eyeglass and window coatings, and the like. These compounds can be organic or inorganic in nature. For example, transparent iron oxides, also known as trans-oxides, have been used in paints and stains.
In one example, U.S. Pat. No. 6,818,050 B1 discloses the use of oxides, including transparent oxides, along with at least one organic or inorganic white, black, or chromatic pigment such as zinc oxide, in lacquers, paints and other coating systems. Zinc oxide can be used for different purposes, depending upon the particle size of the zinc oxide. Zinc oxide is a known white pigment when used in paints, sunscreens, and architectural coatings, but these zinc oxide particles typically include relatively large particles that impart a white color to a composition.
On the other hand, other metal oxides, e.g., cerium oxide particles, when possessing a relatively small particle size, do not generally impart a white color to a composition and have recently been used as UV protectants in coatings and bulk materials. For instance, European Patent Application No. EP 0 732 356 A2 discloses acrylic coatings on a thermoplastic substrate containing cerium oxide as an inorganic UV light absorber. This publication also discloses that the cerium oxide can be added as an aquasol or an organosol to an acrylic primer to protect the thermoplastic substrate.
Similarly, U.S. Pat. No. 6,790,273 B1 discloses compositions comprising inorganic UV absorbers including nano-CeO2 to protect materials such as plastics from photochemical degradation. This patent also discloses that the compositions contain more than 15% nano-CeO2. This patent further discloses the use of these nano-CeO2 particles in combination with polyfunctional organosilanes and polymers made therefrom.
There are several publications in the patent literature that describe combinations of metal oxides with organosilanes and/or polymers made therefrom, including reaction products of organosilanes and metal oxides, such as organosilane-grafted metal oxides. For example, U.S. Pat. No. 6,264,859 B1 discloses optically transparent UV-protective coatings comprising cerium oxide in an inorganic oxide matrix formed by the hydrolysis and condensation of an organoalkoxysilane and/or other metal alkoxide, in combination with the reaction product of cerium oxide and tetraalkylsilicate.
U.S. Pat. No. 6,846,572 B1 discloses compositions used to form coatings in which a metal oxide bonded to a silanol-containing or silanol-forming group is used in combination with a melamine compound to form a cured product or laminate. Other similar patent publications include U.S. Patent Application Publication Nos. 2003/0073779 A1 and 2004/0254282 A1, as well as U.S. Pat. Nos. 6,214,416 B1 and 6,756,124 B1. For instance, U.S. Patent Application Publication No. 2003/0073779 A1 discloses an aqueous dispersion and coated product produced therefrom containing a metal oxide and an organosilane or a hydrolysate of an organosilane, as well as other components.
In some cases, combinations of components can be found to have increased effect when combined under certain circumstances. For instance, U.S. Pat. No. 6,627,180 B1 to L'Oreal describes a topically applicable cosmetic/dermatological sunscreen composition containing mixed UV-photoprotecting screening agents.
However, in architectural coating applications, such as for use with paints and stains, there remains a need involving industrial coatings to increase the UV-protective ability of coating compositions.